Key fastening system



FIG. 1 is a perspective view of a key fastening system showing our new design;

FIG. 2 is a side elevational view;

FIG. 3 is a front elevational view;

FIG. 4 is a top plan view; and,

FIG. 5 is a bottom plan view. 

The ornamental design for a key fastening system, as shown. 